Probing carrier lifetimes in photovoltaic materials using subsurface two-photon microscopy.

Accurately measuring the bulk minority carrier lifetime is one of the greatest challenges in evaluating photoactive materials used in photovoltaic cells. One-photon time-resolved photoluminescence decay measurements are commonly used to measure lifetimes of direct bandgap materials. However, because the incident photons have energies higher than the bandgap of the semiconductor, most carriers are generated close to the surface, where surface defects cause inaccurate lifetime measurements.

Self-limited plasmonic welding of silver nanowire junctions.

Nanoscience provides many strategies to construct high-performance materials and devices, including solar cells, thermoelectrics, sensors, transistors, and transparent electrodes. Bottom-up fabrication facilitates large-scale chemical synthesis without the need for patterning and etching processes that waste material and create surface defects. However, assembly and contacting procedures still require further development.

CuInS(2) solar cells by air-stable ink rolling.

Solution-based deposition techniques are widely considered to be a route to low-cost, high-throughput photovoltaic device fabrication. In this report, we establish a methodology for a highly scalable deposition process and report the synthesis of an air-stable, vulcanized ink from commercially available precursors. Using our air-stable ink rolling (AIR) process, we can make solar cells with an absorber layer that is flat, contaminant-free, and composed of large-grained CuInS(2).

Phase transformation of biphasic Cu2S-CuInS2 to monophasic CuInS2 nanorods.

We synthesized wurtzite CuInS(2) nanorods (NRs) by colloidal solution-phase growth. We discovered that the growth process starts with nucleation of Cu(2)S nanodisks, followed by epitaxial overgrowth of CuInS(2) NRs onto only one face of Cu(2)S nanodisks, resulting in biphasic Cu(2)S-CISu heterostructured NRs. The phase transformation of biphasic Cu(2)S-CuInS(2) into monophasic CuInS(2) NRs occurred with growth progression.

Efficient multiple exciton generation observed in colloidal PbSe quantum dots with temporally and spectrally resolved intraband excitation.

We have spectrally resolved the intraband transient absorption of photogenerated excitons to quantify the exciton population dynamics in colloidal PbSe quantum dots (QDs). These measurements demonstrate that the spectral distribution, as well as the amplitude, of the transient spectrum depends on the number of excitons excited in a QD. To accurately quantify the average number of excitons per QD, the transient spectrum must be spectrally integrated.

Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays.

Hydrogenated amorphous Si (a-Si:H) is an important solar cell material. Here we demonstrate the fabrication of a-Si:H nanowires (NWs) and nanocones (NCs), using an easily scalable and IC-compatible process. We also investigate the optical properties of these nanostructures.

Solution-processed metal nanowire mesh transparent electrodes.

Transparent conductive electrodes are important components of thin-film solar cells, light-emitting diodes, and many display technologies. Doped metal oxides are commonly used, but their optical transparency is limited for films with a low sheet resistance. Furthermore, they are prone to cracking when deposited on flexible substrates, are costly, and require a high-temperature step for the best performance.